Method for processing loss of access in a wireless communication system, and device therefor

ABSTRACT

Disclosed are a method for processing a loss of access wherein a first network entity of a first network determines, from a measurement report of a terminal operating by SCM or TSCM, a loss of access of the terminal to the first network, and notifies a second network entity of the loss of access, and a method for processing a loss of access wherein, when the loss of access of the terminal is received, the second network entity processes the loss of access according to whether a condition for dropping a loss of access is satisfied.

TECHNICAL FIELD

The present invention relates to a wireless communication system, andmore particularly, to a method for processing access loss of a userequipment and a device therefor.

BACKGROUND ART

Wireless access systems have been widely deployed to provide varioustypes of communication services such as voice or data. In general, awireless access system is a multiple access system that may supportcommunication of multiple users by sharing available system resources(e.g., a bandwidth, transmission power, etc.). For example, multipleaccess systems include a Code Division Multiple Access (CDMA) system, aFrequency Division Multiple Access (FDMA) system, a Time DivisionMultiple Access (TDMA) system, an Orthogonal Frequency Division MultipleAccess (OFDMA) system, a Single Carrier Frequency Division MultipleAccess (SC-FDMA) system, and a multi carrier frequency division multipleaccess (MC-FDMA) system.

DISCLOSURE Technical Problem

An object of the present invention is to suggest a mechanism thatefficiently processes access loss of a user equipment (UE) in a mobilecommunication system such as 3GPP or WLAN (Wireless Local Area Network).

Another object of the present invention is to suggest conditions fordetermining access loss of a UE to allow a network node to determine theaccess loss quickly and efficiently.

Other object of the present invention is to reduce signaling overhead ofa network by setting conditions for dropping access loss of a UE.

The technical problems solved by the present invention are not limitedto the above technical problems and other technical problems which arenot described herein will become apparent to those skilled in the artfrom the following description.

Technical Solution

A method for processing access loss of a first network entity to solvethe technical problems comprises the steps of receiving a measurementreport from a user equipment (UE) operating by simultaneously accessinga first network and a second network; transmitting data to the UE if itis determined that handover is not required for the UE on the basis ofthe measurement report; determining that access loss of the UE for thefirst network has been generated if an acknowledgement (ACK) signal forthe data is not received from the UE for a predetermined time; andtransmitting the access loss of the UE for the first network to a secondnetwork entity operating on the first network.

The method may further comprise the step of determining that access lossof the UE for the first network has been generated if an ACK signal forthe data transmitted to the UE is not received from the UE for apredetermined time in a state that the measurement report is notreceived.

The first network may be a 3GPP network, the second network may be aWLAN (Wireless Local Area Network), the first network entity may be aneNB (evolved NodeB) operating on the first network, and the secondnetwork entity may be an MME (Mobility Management Entity) operating onthe first network.

A first network entity to solve the technical problems comprises atransmitter; a receiver; and a processor operating by being connectedwith the transmitter and the receiver, wherein the processor controlsthe receiver to receive a measurement report from a UE operating bysimultaneously accessing a first network and a second network, controlsthe transmitter to transmit data to the UE if it is determined thathandover is not required for the UE on the basis of the measurementreport, determines that access loss of the UE for the first network hasbeen generated if an acknowledgement (ACK) signal for the data is notreceived from the UE for a predetermined time, and controls thetransmitter to transmit the access loss of the UE for the first networkto a second network entity operating on the first network.

A method for processing access loss by means of a second network entityto solve the technical problems comprises the steps of receivinginformation indicating access loss of a UE for a first network from afirst network entity operating on the first network; determining whetherat least one of conditions for dropping the access loss is satisfied;and processing that the access of the UE for the first network is lostif the condition is not satisfied.

The method for processing access loss may further comprise the step ofdisregarding the information indicating access loss if at least one ofthe conditions is satisfied.

The conditions include a case that the first network entity which hastransmitted the information indicating access loss is different from anentity stored in context information owned by the second network entitywith respect to the UE, a case that the first network entity isrequested from another network node to provide the context informationowned with respect to the UE, and a case that the second network entitydoes not own the content information with respect to the UE.

The method for processing access loss may further comprise the step ofreceiving information indicating processing of the access loss inaccordance with an operating mode of the UE from a packet data networkgateway (PGW), wherein the step of determining whether the condition issatisfied may include determining whether the condition for dropping theaccess loss is satisfied only if the UE is operating in the singleconnection mode (SCM) or transparent SCM (TSCM) by identifyingsubscription information of the UE.

The method for processing access loss may further comprise the step ofgenerating a plurality of groups on the basis of subscriptioninformation owned by the second network entity, and the step ofdetermining whether the condition is satisfied may be performed only ifthe UE belongs to a group determined to process the access loss amongthe plurality of groups.

The method for processing access loss may further comprise the step ofreceiving information indicating processing of the access loss from thePGW depending on whether PDN (Packet Data Network) connection of the UEsupports NBIFOM (Network Based IP Flow Mobility), and the step ofdetermining whether the condition is satisfied may include determiningwhether the condition for dropping the access loss is satisfied only ifPDN connection of the UE supports the NBIFOM by identifying subscriptioninformation of the UE.

The processing step may further include the step of transmitting theinformation indicating access loss to a third network entity operatingon the first network if the condition is not satisfied.

The first network may be a 3GPP network, the second network may be aWLAN (Wireless Local Area Network), the first network entity may be aneNB (evolved NodeB) operating on the first network, the second networkentity may be an MME (Mobility Management Entity) operating on the firstnetwork, and the third network entity may be an SGW (Serving GateWay)operating on the first network.

A second network entity to solve the technical problems comprises atransmitter; a receiver; and a processor operating by being connectedwith the transmitter and the receiver, wherein the processor controlsthe receiver to receive information indicating the access loss of the UEfor a first network from a first network entity operating on the firstnetwork, determines whether at least one of conditions for dropping theaccess loss is satisfied, and processes that the access of the UE forthe first network is lost if the condition is not satisfied.

Advantageous Effects

As is apparent from the above description, the embodiments of thepresent invention have the following effects.

First of all, a path where 3GPP access loss of a UE is notified to anetwork is ensured even in the case that the UE is operated in SCM orTSCM.

Secondly, various conditions for determining access loss of the UE aresuggested, whereby the access loss of the UE can be identified quicklyand exactly.

Thirdly, various entities for determining access loss of the UE aresuggested, whereby signaling overhead may be minimized even in the casethat the access loss is determined in error.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinmay be derived by those skilled in the art from the followingdescription of the embodiments of the present invention. That is,effects which are not intended by the present invention may be derivedby those skilled in the art from the embodiments of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate embodiments of the inventionand together with the description serve to explain the principle of theinvention. The technical features of the present invention are notlimited to specific drawings and the features shown in the drawings arecombined to construct a new embodiment. Reference numerals of thedrawings mean structural elements.

FIG. 1 is a diagram illustrating a brief structure of an evolved packetsystem (EPS) that includes an evolved packet core (EPC).

FIG. 2 is an exemplary diagram illustrating an architecture of a generalE-UTRAN and a general EPC.

FIG. 3 is an exemplary diagram illustrating a structure of a radiointerface protocol on a control plane.

FIG. 4 is an exemplary diagram illustrating a structure of a radiointerface protocol on a user plane.

FIG. 5 is a flow chart illustrating a random access procedure.

FIG. 6 is a diagram illustrating a connection procedure in a radioresource control (RRC) layer.

FIGS. 7 and 8 illustrates an example of a structure of a WLAN connectedto an EPC.

FIG. 9 is an exemplary view illustrating an example of IFOM (IP FlowMobility) technology.

FIGS. 10(a) and 10(b) illustrate a network control entity for accessnetwork selection.

FIG. 11 is a diagram illustrating a structure of a TWAN (TrustedWireless Access Network).

FIG. 12 illustrates a protocol stack between a UE and a TWAN, whichoperate in a single connection mode (SCM).

FIG. 13 illustrates a protocol stack between a UE and a TWAN, whichoperate in a multiple connection mode (MCM).

FIG. 14 illustrates a TWAN initial access procedure of a UE operating ina transparent SCM (TSCM).

FIG. 15 illustrates a TWAN initial access procedure of a UE operating inan SCM.

FIG. 16 illustrates a procedure of processing 3GPP access loss in a UEoperating in MCM.

FIG. 17 illustrates a procedure of processing WLAN access loss.

FIG. 18 illustrates an example of a procedure of processing access lossin a network node.

FIG. 19 illustrates another example of a procedure of processing accessloss in a network node.

FIG. 20 illustrates other example of a procedure of processing accessloss in a network node.

FIG. 21 illustrates a procedure of notifying an MME whether a PDNgateway (PGW) supports a connection mode of a UE and NBIFOM andprocessing access loss in a specific condition only.

FIG. 22 is a diagram illustrating an example of a procedure ofprocessing 3GPP access loss when the 3GPP access loss is sensed.

FIG. 23 is a diagram illustrating an example of a procedure ofprocessing WLAN access loss when the WLAN access loss is sensed.

FIG. 24 is a diagram illustrating an example of a method for processingdata when 3GPP access loss is sensed.

FIG. 25 is a diagram illustrating an example of a method for processingdata when WLAN access loss is sensed.

FIG. 26 is a diagram illustrating another example of a method forprocessing data when 3GPP access loss is sensed.

FIG. 27 is a diagram illustrating a configuration of a node deviceaccording to the embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Although the terms used in the present invention are selected fromgenerally known and used terms, terms used herein may be varieddepending on operator's intention or customs in the art, appearance ofnew technology, or the like. In addition, some of the terms mentioned inthe description of the present invention have been selected by theapplicant at his or her discretion, the detailed meanings of which aredescribed in relevant parts of the description herein. Furthermore, itis required that the present invention is understood, not simply by theactual terms used but by the meanings of each term lying within.

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered optional factors on the conditionthat there is no additional remark. If required, the individualconstituent components or characteristics may not be combined with othercomponents or characteristics. In addition, some constituent componentsand/or characteristics may be combined to implement the embodiments ofthe present invention. The order of operations to be disclosed in theembodiments of the present invention may be changed. Some components orcharacteristics of any embodiment may also be included in otherembodiments, or may be replaced with those of the other embodiments asnecessary.

In describing the present invention, if it is determined that thedetailed description of a related known function or construction rendersthe scope of the present invention unnecessarily ambiguous, the detaileddescription thereof will be omitted.

In the entire specification, when a certain portion “comprises orincludes” a certain component, this indicates that the other componentsare not excluded and may be further included unless specially describedotherwise. The terms “unit”, “-or/er” and “module” described in thespecification indicate a unit for processing at least one function oroperation, which may be implemented by hardware, software or acombination thereof. The words “a or an”, “one”, “the” and words relatedthereto may be used to include both a singular expression and a pluralexpression unless the context describing the present invention(particularly, the context of the following claims) clearly indicatesotherwise.

The embodiments of the present invention can be supported by thestandard documents disclosed in any one of wireless access systems, suchas an IEEE 802.xx system, a 3rd Generation Partnership Project (3GPP)system, a 3GPP Long Term Evolution (LTE) system, and a 3GPP2 system.That is, the steps or portions, which are not described in order to makethe technical spirit of the present invention clear, may be supported bythe above documents.

In addition, all the terms disclosed in the present document may bedescribed by the above standard documents. In particular, theembodiments of the present invention may be supported by at least one ofTS 23.161, TS 23.401, TS 23.402, TS 24.301, TS 24.302, TS 29.274, TS36.300 and TS 36.331, which are the standard documents of the 3GPPsystem, and P802.16e-2004, P802.16e-2005, P802.16.1, P802.16p andP802.16.1b, which are the standard documents of the IEEE 802.16 system.

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings. It is to beunderstood that the detailed description which will be disclosed alongwith the accompanying drawings is intended to describe the exemplaryembodiments of the present invention, and is not intended to describe aunique embodiment which the present invention can be carried out.

It should be noted that specific terms disclosed in the presentinvention are proposed for convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to another format within the technical scope orspirit of the present invention.

First of all, the terms used in this specification can be defined asfollows.

-   -   UMTS (Universal Mobile Telecommunications System): a GSM (Global        System for Mobile Communication) based third generation mobile        communication technology developed by the 3GPP.    -   EPS (Evolved Packet System): a network system that includes an        EPC (Evolved Packet Core) which is an IP (Internet Protocol)        based packet switched core network and an access network such as        LTE and UTRAN. This system is the network of an evolved version        of the UMTS.    -   NodeB: a base station of GERAN/UTRAN. This base station is        installed outdoor and its coverage has a scale of a macro cell.    -   eNodeB: a base station of LTE. This base station is installed        outdoor and its coverage has a scale of a macro cell.    -   UE (User Equipment): the UE may be referred to as terminal, ME        (Mobile Equipment), MS (Mobile Station), etc. Also, the UE may        be a portable device such as a notebook computer, a cellular        phone, a PDA (Personal Digital Assistant), a smart phone, and a        multimedia device. Alternatively, the UE may be a non-portable        device such as a PC (Personal Computer) and a vehicle mounted        device. The term “UE”, as used in relation to MTC, can refer to        an MTC device.    -   HNB (Home NodeB): a base station of UMTS network. This base        station is installed indoor and its coverage has a scale of a        micro cell.    -   HeNB (Home eNodeB): a base station of an EPS network. This base        station is installed indoor and its coverage has a scale of a        micro cell.    -   MME (Mobility Management Entity): a network node of an EPS        network, which performs mobility management (MM) and session        management (SM).    -   PDN-GW (Packet Data Network-Gateway)/PGW: a network node of an        EPS network, which performs UE IP address allocation, packet        screening and filtering, charging data collection, etc.    -   SGW (Serving Gateway): a network node of an EPS network, which        performs mobility anchor, packet routing, idle-mode packet        buffering, and triggering of an MME's UE paging.    -   NAS (Non-Access Stratum): an upper stratum of a control plane        between a UE and an MME. This is a functional layer for        transmitting and receiving a signaling and traffic message        between a UE and a core network in an LTE/UMTS protocol stack,        and supports mobility of a UE, and supports a session management        procedure of establishing and maintaining IP connection between        a UE and a PDN GW.    -   PDN (Packet Data Network): a network in which a server        supporting a specific service (e.g., a Multimedia Messaging        Service (MMS) server, a Wireless Application Protocol (WAP)        server, etc.) is located.    -   PDN connection: a logical connection between a UE and a PDN,        represented as one IP address (one IPv4 address and/or one IPv6        prefix).    -   RAN (Radio Access Network): a unit including a Node B, an eNode        B, and a Radio Network Controller (RNC) for controlling the Node        B and the eNode B in a 3GPP network, which is present between        UEs and provides a connection to a core network.    -   HLR (Home Location Register)/HSS (Home Subscriber Server): a        database having subscriber information in a 3GPP network. The        HSS can perform functions such as configuration storage,        identity management, and user state storage.    -   PLMN (Public Land Mobile Network): a network configured for the        purpose of providing mobile communication services to        individuals. This network can be configured per operator.    -   ANDSF (Access Network Discovery and Selection Function): This is        one of network entities for providing a policy for discovering        and selecting an access that can be used by a UE on an operator        basis.    -   ISRP (Inter-System Routing Policy): This is a protocol defined        by the operator to indicate which one will be used by the UE for        routing of IP traffic among several radio access interfaces. The        ISRP may include three types of protocols as follows, as a        policy for defining an access network preferred (i.e., having a        high priority) or restricted to route/steer a packet service (or        an IP flow or IP traffic or applications). That is, the ISRP may        be divided into an IP flow mobility (IFOM) protocol, a multi        access PDN connectivity (MAPCON) protocol, and a non-seamless        WLAN offload (NSWO) protocol as follows.    -   IFOM (IP Flow Mobility) protocol: This protocol is in regards to        a list in which access technologies/access networks to be used        by the UE are arranged according to a priority, when traffic        matched to a specific IP traffic filter can be routed on a        specific APN (Access Point Name) or on a random APN. Further,        this protocol may designate for which radio access the traffic        matched to the specific IP traffic filter is limited on the        specific APN or on the random APN.    -   MAPCON (Multi Access PDN Connectivity) protocol: This protocol        is a list in which the access technologies/access networks to be        used by the UE are arranged according to the priority when a PDN        connection for the specific APN can be routed. Further, this        protocol may designate for which radio access a PDN connection        to a specific APN will be limited.    -   NSWO(Non-seamless WLAN offload) protocol: This protocol        designates whether certain traffic will be offloaded or not        offloaded non-seamlessly to a WLAN.    -   ISMP (Inter-System Mobility Policy): This is a set of protocols        defined by an operator to have an impact on an inter-system        mobility decision made by the UE. When the UE can route IP        traffic on a single radio access interface, the UE may use ISMP        to select the most appropriate access technology type or access        network in a given time.    -   RAN rule: This is a rule received from the network and is called        RAN support information. The RAN rule is also called WLAN        interworking supported by the RAN used without ANDSF ISRP/ISMP.        When the RAN rule for moving traffic to the WLAN is satisfied,        an access stratum (AS) layer of the UE delivers a        move-traffic-to-WLAN indication and a WLAN identifier together        to a higher layer of the UE. Alternatively, when the RAN rule        for moving the traffic to the 3GPP access is satisfied, the AS        layer of the UE delivers a move-traffic-from-WLAN indication to        the higher layer of the UE. 3GPP. 3GPP TS 23.401, TS 23.060, TS        23.402, TS 36.300, TS 36.304, TS 36.331, TS 25.304, and TS        25.331 may be incorporated herein for detailed descriptions on        the RAN rule.    -   Local Operating Environment Information: This is a set of        implementation specific parameters which describe the local        environment in which the UE is operating.    -   Network-Based IP Flow Mobility(NBIFOM): This is IP flow mobility        based on network based mobility protocol (GTP or PMIP).    -   UE-initiated NBIFOM: This is NBIFOM in which the UE initiates IP        flow mobility.    -   Network-initiated NBIFOM: This is NBIFOM in which the network        initiates IP flow mobility.    -   Multi-access PDN connection: This is a PDN connection in which        traffic can be routed through the 3GPP access and/or the WLAN        access. Each IP flow is routed only through one access at one        instance.    -   Routing filter: This is a set of IP header parameter        values/ranges of a packet flow used to identify IP flow for the        purpose of routing.    -   Routing access type: This is a type of an access for routing a        set of IP flows of PDN connection (3GPP access or WLAN access.    -   Routing Rule (RR): This is a set of information that enables        association between the routing filter and the routing access        type.

1. Evolved Packet Core (EPC)

FIG. 1 is a schematic diagram showing the structure of an evolved packetsystem (EPS) including an evolved packet core (EPC).

The EPC is a core element of system architecture evolution (SAE) forimproving performance of 3GPP technology. SAE corresponds to a researchproject for determining a network structure supporting mobility betweenvarious types of networks. For example, SAE aims to provide an optimizedpacket-based system for supporting various radio access technologies andproviding an enhanced data transmission capability.

Specifically, the EPC is a core network of an IP mobile communicationsystem for 3GPP LTE and can support real-time and non-real-timepacket-based services. In conventional mobile communication systems(i.e. second-generation or third-generation mobile communicationsystems), functions of a core network are implemented through acircuit-switched (CS) sub-domain for voice and a packet-switched (PS)sub-domain for data. However, in a 3GPP LTE system which is evolved fromthe third generation communication system, CS and PS sub-domains areunified into one IP domain. That is, in 3GPP LTE, connection ofterminals having IP capability can be established through an IP-basedbusiness station (e.g., an eNodeB (evolved Node B)), EPC, and anapplication domain (e.g., IMS). That is, the EPC is an essentialstructure for end-to-end IP services.

The EPC may include various components. FIG. 1 shows some of thecomponents, namely, a serving gateway (SGW), a packet data networkgateway (PDN GW), a mobility management entity (MME), a serving GPRS(general packet radio service) supporting node (SGSN) and an enhancedpacket data gateway (ePDG).

The SGW operates as a boundary point between a radio access network(RAN) and a core network and maintains a data path between an eNodeB andthe PDN GW. When. When a terminal moves over an area served by aneNodeB, the SGW functions as a local mobility anchor point. That is,packets. That is, packets may be routed through the SGW for mobility inan evolved UMTS terrestrial radio access network (E-UTRAN) defined after3GPP release-8. In addition, the SGW may serve as an anchor point formobility of another 3GPP network (a RAN defined before 3GPP release-8,e.g., UTRAN or GERAN (global system for mobile communication(GSM)/enhanced data rates for global evolution (EDGE) radio accessnetwork).

The PDN GW corresponds to a termination point of a data interface for apacket data network. The PDN GW may support policy enforcement features,packet filtering and charging support. In addition, the PDN GW may serveas an anchor point for mobility management with a 3GPP network and anon-3GPP network (e.g., an unreliable network such as an interworkingwireless local area network (I-WLAN) and a reliable network such as acode division multiple access (CDMA) or WiMax network).

Although the SGW and the PDN GW are configured as separate gateways inthe example of the network structure of FIG. 1, the two gateways may beimplemented according to a single gateway configuration option.

The MME performs signaling and control functions for supporting accessof a UE for network connection, network resource allocation, tracking,paging, roaming and handover. The MME controls control plane functionsassociated with subscriber and session management. The MME managesnumerous eNodeBs and signaling for selection of a conventional gatewayfor handover to other 2G/3G networks. In addition, the MME performssecurity procedures, terminal-to-network session handling, idle terminallocation management, etc.

The SGSN handles all packet data such as mobility management andauthentication of a user for other 3GPP networks (e.g., a GPRS network).

The ePDG serves as a security node for a non-3GPP network (e.g., anI-WLAN, a Wi-Fi hotspot, etc.).

As described above with reference to FIG. 1, a terminal having IPcapabilities may access an IP service network (e.g., an IMS) provided byan operator via various elements in the EPC not only based on 3GPPaccess but also on non-3GPP access.

Additionally, FIG. 1 shows various reference points (e.g. S1-U, S1-MME,etc.). In 3GPP, a conceptual link connecting two functions of differentfunctional entities of an E-UTRAN and an EPC is defined as a referencepoint. Table 1 is a list of the reference points shown in FIG. 1.Various reference points may be present in addition to the referencepoints in Table 1 according to network structures.

TABLE 1 Reference point Description S1-MME Reference point for thecontrol plane protocol between E-UTRAN and MME S1-U Reference pointbetween E-UTRAN and Serving GW for the per bearer user plane tunnelingand inter eNodeB path switching during handover S3 It enables user andbearer information exchange for inter 3GPP access network mobility inidle and/or active state. This reference point can be used intra-PLMN orinter-PLMN (e.g. in the case of Inter-PLMN HO). S4 It provides relatedcontrol and mobility support between GPRS Core and the 3GPP Anchorfunction of Serving GW. In addition, if Direct Tunnel is notestablished, it provides the user plane tunneling. S5 It provides userplane tunneling and tunnel management between Serving GW and PDN GW. Itis used for Serving GW relocation due to UE mobility and if the ServingGW needs to connect to a non-collocated PDN GW for the required PDNconnectivity. S11 Reference point between an MME and an SGW SGi It isthe reference point between the PDN GW and the packet data network.Packet data network may be an operator external public or private packetdata network or an intra operator packet data network, e.g. forprovision of IMS services. This reference point corresponds to Gi for3GPP accesses.

Among the reference points shown in FIG. 1, S2a and S2b correspond tonon-3GPP interfaces. S2a is a reference point which provides reliablenon-3GPP access and related control and mobility support between PDN GWsto a user plane. S2b is a reference point which provides related controland mobility support between the ePDG and the PDN GW to the user plane.

FIG. 2 is a diagram exemplarily illustrating architectures of a typicalE-UTRAN and EPC.

As shown in the figure, while radio resource control (RRC) connection isactivated, an eNodeB may perform routing to a gateway, schedulingtransmission of a paging message, scheduling and transmission of abroadcast channel (BCH), dynamic allocation of resources to a UE onuplink and downlink, configuration and provision of eNodeB measurement,radio bearer control, radio admission control, and connection mobilitycontrol. In the EPC, paging generation, LTE_IDLE state management,ciphering of the user plane, SAE bearer control, and ciphering andintegrity protection of NAS signaling.

FIG. 3 is a diagram exemplarily illustrating the structure of a radiointerface protocol in a control plane between a UE and a base station,and FIG. 4 is a diagram exemplarily illustrating the structure of aradio interface protocol in a user plane between the UE and the basestation.

The radio interface protocol is based on the 3GPP wireless accessnetwork standard. The radio interface protocol horizontally includes aphysical layer, a data link layer, and a networking layer. The radiointerface protocol is divided into a user plane for transmission of datainformation and a control plane for delivering control signaling whichare arranged vertically.

The protocol layers may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on the three sublayers of theopen system interconnection (OSI) model that is well known in thecommunication system.

Hereinafter, description will be given of a radio protocol in thecontrol plane shown in FIG. 3 and a radio protocol in the user planeshown in FIG. 4.

The physical layer, which is the first layer, provides an informationtransfer service using a physical channel. The physical channel layer isconnected to a medium access control (MAC) layer, which is a higherlayer of the physical layer, through a transport channel Data istransferred between the physical layer and the MAC layer through thetransport channel Transfer of data between different physical layers,i.e., a physical layer of a transmitter and a physical layer of areceiver is performed through the physical channel.

The physical channel consists of a plurality of subframes in the timedomain and a plurality of subcarriers in the frequency domain. Onesubframe consists of a plurality of symbols in the time domain and aplurality of subcarriers. One subframe consists of a plurality ofresource blocks. One resource block consists of a plurality of symbolsand a plurality of subcarriers. A Transmission Time Interval (TTI), aunit time for data transmission, is 1 ms, which corresponds to onesubframe.

According to 3GPP LTE, the physical channels present in the physicallayers of the transmitter and the receiver may be divided into datachannels corresponding to Physical Downlink Shared Channel (PDSCH) andPhysical Uplink Shared Channel (PUSCH) and control channelscorresponding to Physical Downlink Control Channel (PDCCH), PhysicalControl Format Indicator Channel (PCFICH), Physical Hybrid-ARQ IndicatorChannel (PHICH) and Physical Uplink Control Channel (PUCCH).

The second layer includes various layers. First, the MAC layer in thesecond layer serves to map various logical channels to various transportchannels and also serves to map various logical channels to onetransport channel. The MAC layer is connected with an RLC layer, whichis a higher layer, through a logical channel. The logical channel isbroadly divided into a control channel for transmission of informationof the control plane and a traffic channel for transmission ofinformation of the user plane according to the types of transmittedinformation.

The radio link control (RLC) layer in the second layer serves to segmentand concatenate data received from a higher layer to adjust the size ofdata such that the size is suitable for a lower layer to transmit thedata in a radio interval.

The Packet Data Convergence Protocol (PDCP) layer in the second layerperforms a header compression function of reducing the size of an IPpacket header which has a relatively large size and contains unnecessarycontrol information, in order to efficiently transmit an IP packet suchas an IPv4 or IPv6 packet in a radio interval having a narrow bandwidth.In addition, in LTE, the PDCP layer also performs a security function,which consists of ciphering for preventing a third party from monitoringdata and integrity protection for preventing data manipulation by athird party.

The Radio Resource Control (RRC) layer, which is located at theuppermost part of the third layer, is defined only in the control plane,and serves to configure radio bearers (RBs) and control a logicalchannel, a transport channel, and a physical channel in relation toreconfiguration and release operations. The RB represents a serviceprovided by the second layer to ensure data transfer between a UE andthe E-UTRAN.

If an RRC connection is established between the RRC layer of the UE andthe RRC layer of a wireless network, the UE is in the RRC Connectedmode. Otherwise, the UE is in the RRC Idle mode.

Hereinafter, description will be given of the RRC state of the UE and anRRC connection method. The RRC state refers to a state in which the RRCof the UE is or is not logically connected with the RRC of the E-UTRAN.The RRC state of the UE having logical connection with the RRC of theE-UTRAN is referred to as an RRC_CONNECTED state. The RRC state of theUE which does not have logical connection with the RRC of the E-UTRAN isreferred to as an RRC_IDLE state. A UE in the RRC_CONNECTED state hasRRC connection, and thus the E-UTRAN may recognize presence of the UE ina cell unit. Accordingly, the UE may be efficiently controlled. On theother hand, the E-UTRAN cannot recognize presence of a UE which is inthe RRC_IDLE state. The UE in the RRC_IDLE state is managed by a corenetwork in a tracking area (TA) which is an area unit larger than thecell. That is, for the UE in the RRC_IDLE state, only presence orabsence of the UE is recognized in an area unit larger than the cell. Inorder for the UE in the RRC_IDLE state to be provided with a usualmobile communication service such as a voice service and a data service,the UE should transition to the RRC_CONNECTED state. A TA isdistinguished from another TA by a tracking area identity (TAI) thereof.A UE may configure the TAI through a tracking area code (TAC), which isinformation broadcast from a cell.

When the user initially turns on the UE, the UE searches for a propercell first. Then, the UE establishes RRC connection in the cell andregisters information thereabout in the core network. Thereafter, the UEstays in the RRC_IDLE state. When necessary, the UE staying in theRRC_IDLE state selects a cell (again) and checks system information orpaging information. This operation is called camping on a cell. Onlywhen the UE staying in the RRC_IDLE state needs to establish RRCconnection, does the UE establish RRC connection with the RRC layer ofthe E-UTRAN through the RRC connection procedure and transition to theRRC_CONNECTED state. The UE staying in the RRC_IDLE state needs toestablish RRC connection in many cases. For example, the cases mayinclude an attempt of a user to make a phone call, an attempt totransmit data, or transmission of a response message after reception ofa paging message from the E-UTRAN.

The non-access stratum (NAS) layer positioned over the RRC layerperforms functions such as session management and mobility management.

Hereinafter, the NAS layer shown in FIG. 3 will be described in detail.

The eSM (evolved Session Management) belonging to the NAS layer performsfunctions such as default bearer management and dedicated bearermanagement to control a UE to use a PS service from a network. The UE isassigned a default bearer resource by a specific packet data network(PDN) when the UE initially accesses the PDN. In this case, the networkallocates an available IP to the UE to allow the UE to use a dataservice. The network also allocates QoS of a default bearer to the UE.LTE supports two kinds of bearers. One bearer is a bearer havingcharacteristics of guaranteed bit rate (GBR) QoS for guaranteeing aspecific bandwidth for transmission and reception of data, and the otherbearer is a non-GBR bearer which has characteristics of best effort QoSwithout guaranteeing a bandwidth. The default bearer is assigned to anon-GBR bearer. The dedicated bearer may be assigned a bearer having QoScharacteristics of GBR or non-GBR.

A bearer allocated to the UE by the network is referred to as an evolvedpacket service (EPS) bearer. When the EPS bearer is allocated to the UE,the network assigns one ID. This ID is called an EPS bearer ID. One EPSbearer has QoS characteristics of a maximum bit rate (MBR) and/or aguaranteed bit rate (GBR).

FIG. 5 is a flowchart illustrating a random access procedure in 3GPPLTE.

The random access procedure is performed for a UE to obtain ULsynchronization with an eNB or to be assigned a UL radio resource.

The UE receives a root index and a physical random access channel(PRACH) configuration index from an eNodeB. Each cell has 64 candidaterandom access preambles defined by a Zadoff-Chu (ZC) sequence. The rootindex is a logical index used for the UE to generate 64 candidate randomaccess preambles.

Transmission of a random access preamble is limited to a specific timeand frequency resources for each cell. The PRACH configuration indexindicates a specific subframe and preamble format in which transmissionof the random access preamble is possible.

The UE transmits a randomly selected random access preamble to theeNodeB. The UE selects a random access preamble from among 64 candidaterandom access preambles and the UE selects a subframe corresponding tothe PRACH configuration index. The UE transmits the selected randomaccess preamble in the selected subframe.

Upon receiving the random access preamble, the eNodeB sends a randomaccess response (RAR) to the UE. The RAR is detected in two steps.First, the UE detects a PDCCH masked with a random access (RA)-RNTI. TheUE receives an RAR in a MAC (medium access control) PDU (protocol dataunit) on a PDSCH indicated by the detected PDCCH.

FIG. 6 illustrates a connection procedure in a radio resource control(RRC) layer.

As shown in FIG. 6, the RRC state is set according to whether or not RRCconnection is established. An RRC state indicates whether or not anentity of the RRC layer of a UE has logical connection with an entity ofthe RRC layer of an eNodeB. An RRC state in which the entity of the RRClayer of the UE is logically connected with the entity of the RRC layerof the eNodeB is called an RRC connected state. An RRC state in whichthe entity of the RRC layer of the UE is not logically connected withthe entity of the RRC layer of the eNodeB is called an RRC idle state.

A UE in the Connected state has RRC connection, and thus the E-UTRAN mayrecognize presence of the UE in a cell unit. Accordingly, the UE may beefficiently controlled. On the other hand, the E-UTRAN cannot recognizepresence of a UE which is in the idle state. The UE in the idle state ismanaged by the core network in a tracking area unit which is an areaunit larger than the cell. The tracking area is a unit of a set ofcells. That is, for the UE which is in the idle state, only presence orabsence of the UE is recognized in a larger area unit. In order for theUE in the idle state to be provided with a usual mobile communicationservice such as a voice service and a data service, the UE shouldtransition to the connected state.

When the user initially turns on the UE, the UE searches for a propercell first, and then stays in the idle state. Only when the UE stayingin the idle state needs to establish RRC connection, the UE establishesRRC connection with the RRC layer of the eNodeB through the RRCconnection procedure and then performs transition to the RRC connectedstate.

The UE staying in the idle state needs to establish RRC connection inmany cases. For example, the cases may include an attempt of a user tomake a phone call, an attempt to transmit data, or transmission of aresponse message after reception of a paging message from the E-UTRAN.

In order for the UE in the idle state to establish RRC connection withthe eNodeB, the RRC connection procedure needs to be performed asdescribed above. The RRC connection procedure is broadly divided intotransmission of an RRC connection request message from the UE to theeNodeB, transmission of an RRC connection setup message from the eNodeBto the UE, and transmission of an RRC connection setup complete messagefrom the UE to eNodeB, which are described in detail below withreference to FIG. 6.

1) When the UE in the idle state desires to establish RRC connection forreasons such as an attempt to make a call, a data transmission attempt,or a response of the eNodeB to paging, the UE transmits an RRCconnection request message to the eNodeB first.

2) Upon receiving the RRC connection request message from the UE, theENB accepts the RRC connection request of the UE when the radioresources are sufficient, and then transmits an RRC connection setupmessage, which is a response message, to the UE.

3) Upon receiving the RRC connection setup message, the UE transmits anRRC connection setup complete message to the eNodeB. Only when the UEsuccessfully transmits the RRC connection setup message, does the UEestablish RRC connection with the eNodeB and transition to the RRCconnected mode.

2. Connection of WLAN and EPC

FIGS. 7 and 8 illustrate an architecture for connecting a WLAN to anEPC. Specifically, FIG. 7 illustrates an architecture in which a WLAN isconnected to a P-GW through an S2a interface (see 3GPP TS 23.402). Ascan be seen with reference to FIG. 7, a WLAN access network (inparticular, it is a trusted WLAN access network since the S2a interfaceis an interface for connecting a trusted non-3GPP access to the EPC) isconnected to the P-GW through the S2a interface. The content disclosedin TS 23.402 is incorporated herein by reference for an architecture fora trusted WLAN access network (TWAN).

FIG. 8 illustrates an architecture in which a WLAN is connected to aP-GW through an S2b interface. As can be seen with reference to FIG. 8,a WLAN access network (in particular, it is an untrusted WLAN accessnetwork since the S2b interface is an interface for connecting anuntrusted non-3GPP access to the EPC) is connected to the P-GW throughan evolved packet data gateway (ePDG) connected to the P-GW through theS2b interface. Hereinafter, a trusted WLAN and an untrusted WLAN may beboth referred to as a WLAN.

2.1 IFOM

Data of a UE may be offloaded to the WLAN access through a 3GPP access.A technology such as IP flow mobility and seamless offload (IFOM), multiaccess PDN connectivity (MAPCON), or the like has been proposed tosupport a multiple radio access. The MAPCON technology is a technologyof transmitting data by using a 3GPP access and a Wi-Fi access throughrespective PDN connections. The IFOM technology is a technology oftransmitting data by aggregating the 3GPP access and the Wi-Fi access toone PDN or P-GW.

FIG. 9 is an exemplary view of the IFOM technology. Referring to FIG. 9,the IFOM technology is to provide the same PDN connection throughseveral pieces of different accesses. Such IFOM technology providesseamless transmission and reception through offloading onto a WLAN.Furthermore, the IFOM technology provides the transfer of IP flowshaving the same one PDN connection from one access to the other access.As described above, with the help of the technologies capable ofoffloading the traffic of UE onto a WLAN, the congestion of a cellularaccess of a mobile communication service provider can be reduced.

The provider provides a policy to the UE in order to divert the trafficonto the WLAN access and the UE may divert its data onto the wirelessLAN in accordance with the policy. For provision of the policy to theUE, a 3GPP based access network discovery and selection function (ANDSF)may provide a policy associated with the wireless LAN.

FIGS. 10(a) and 10(b) illustrate network control entities for selectingan access network. Referring to FIG. 10(a), the ANDSF may be present inthe home network (Home Public Land Mobile Network (‘HPLMN’)) of the UE.Furthermore, referring to FIG. 10(b), the ANDSF may also be present inthe Visited Public Land Mobile Network (VPLMN) of the UE. When the ANDSFis present in the home network as described above, it may be called anH-ANDSF. When the ANDSF is present in the visited network, it may becalled a V-ANDSF. The ANDSF is used to include the H-ANDSF and/or theV-ANDSF. The ANDSF can provide information on an inter-system movementpolicy (ISMP), information for access network search and information oninter-system routing policy (ISRP), for example, a routing rule.

2.2 TWAN (Trusted Wireless Access Network)

FIG. 11 is a diagram illustrating a structure of a TWAN (TrustedWireless Access Network). As shown in FIG. 11, the TWAN is implementedin such a manner that respective entities for performing each functionare separated from each other. The respective entities implemented to beseparated from each other are connected with another network nodethrough their respective interfaces different from each other. Forexample, a TWAG (Trusted WLAN Access Gateway) is connected to the EPCthrough interface S2a, and a TWAP (Trusted WLAN AAA Proxy) is connectedwith an AAA (Authentication Authorization Accounting) server throughinterface Sta.

2. 3 WLAN Connection Mode

If WLAN access procedure is performed through interface S2a, any one ofTSCM (Transparent Single Connection Mode), SCM (Single Connection Mode)and MCM (Multiple Connection Mode) is selected in accordance withcapabilities of a UE and a network. In the TSCM and the SCM, the UE andthe network may be operated using the existing WLAN-AP as it is but maysimultaneously use only one PDN connection. On the other hand, in theMCM, WLCP (WLAN Control Protocol) should additionally be supported forthe existing WLAN-AP. Likewise, this is equally applied to the UE. Inthe MCM, it is advantageous that several PDCN connections may beconfigured at the same time.

FIG. 12 illustrates a protocol stack between a UE and a TWAN, whichoperate in a single connection mode (SCM). FIG. 13 illustrates aprotocol stack between a UE and a TWAN, which operate in a multipleconnection mode (MCM). As shown in FIG. 13, the MCM may be operated onlyif a WLCP should be supported for both the UE and the TWAN unlike FIG.12. If the WLCP is supported for any one of the UE and the TWAN, theTSCM or the SCM is operated.

Hereinafter, FIGS. 14 and 15 illustrate a TWAN initial access procedureof a UE operating in a transparent SCM (TSCM) and an SCM. FIG. 14illustrates a case of the TSCM, and FIG. 15 illustrates a case of theSCM.

Referring to FIG. 15, a UE operating in the SCM initially attaches tothe TWAN through an initial attach and authentication & authorizationprocedure. In the step of performing a series of authentication andauthorization procedures shown in FIG. 15, PDN connection is generatedbetween the UE and the PGW through steps 12 and 14. In FIG. 16, asignaling for generating PDN connection between the TWAN and the PGW isomitted from FIG. 15, and the authentication & authorization procedureis only shown.

On the other hand, a UE operating in the TSCM in accordance with FIG. 14does not transmit any information for generating PDN connection to thenetwork unlike the UE operating in the SCM, and FIG. 14 is identical toFIG. 15 in that PDN connection is generated between the UE and the PGW.

2.4 Access Loss

FIGS. 16 and 17 respectively illustrate a procedure of processing 3GPPaccess loss and a procedure of processing WLAN access loss.

If access loss for a 3GPP network is generated for a UE which issimultaneously accessing a 3GPP network and a WLAN, the UE notifies thataccess loss for the 3GPP network is generated through access to the WLAN(FIG. 16). The access loss is notified to a policy and charging rulefunction (PCRF) through the PGW, and as the PGW and the PCRF recognizethe access loss, the PGW and the PCRF do not transmit data to the 3GPPnetwork where the access loss is generated, any more. If a routing ruleis accepted, data to the UE is transmitted through another accessnetwork (WLAN) not the 3GPP access network.

On the other hand, if access loss for a WLAN is generated for a UE, theUE notifies that access loss for the WLAN is generated through access tothe 3GPP network (FIG. 17). The access loss is notified to the PGW andthe PCRF in the same manner as FIG. 16, and the PGW and the PCRF do nottransmit data to the WLAN where the access loss is generated, any more.If a routing rule is accepted, data to the UE is transmitted to throughthe 3GPP access network.

3. Suggested Embodiment 1

As described above, if the access loss of the 3GPP network is generated,the UE notifies the TWAN of the access loss of the 3GPP network throughthe WLAN by using the WLCP. The TWAN delivers the access loss of the3GPP network to the PGW. However, unlike the MCM, the WLCP is notsupported if the WLAN is operating in the SCM (or TSCM). Therefore, incase of the UE operating in the SCM, even though the access loss of the3GPP network is generated, a problem occurs in that there is no path fornotifying the PGW of the access loss.

Also, if the access loss of the 3GPP network is generated, data alreadytransmitted to eNB and TWAN before the PGW identifies the access loss ofthe 3GPP network are not delivered to the UE due to the access loss.Therefore, there is no method for again transmitting data transmittedafter the access loss of the 3GPP network is generated, a problem occursin that some data are not received.

Hereinafter, a method for sensing and processing access loss of a 3GPPnetwork or WLAN when the access loss is generated for a UE operating inan SCM (or TSCM) will be suggested. FIG. 22 illustrates an example of aprocedure of processing 3GPP access loss when the 3GPP access loss issensed, and FIG. 23 illustrates an example of a procedure of processingWLAN access loss when the WLAN access loss is sensed. First of all, theexample of the 3GPP access loss will be described with reference to FIG.22.

For application of the aforementioned NBIFOM, the UE should configure aplurality of PDN connections through access to both the 3GPP network andthe WLAN. Therefore, the UE maintains the state of access to the 3GPPnetwork and access to the WLAN. If access loss for the 3GPP network(hereinafter, referred to as 3GPP access loss) or access loss for theWLAN (hereinafter, referred to as WLAN access loss) is generated as theUE is out of coverage of a specific network, this access loss should benotified to the PGW. According to the embodiment suggested below, the3GPP access loss is sensed by the eNB and then notified to the PGW.

First of all, if the UE attaches to the eNB, the eNB establishes the UEto perform measurement report during RRC connection reconfiguration(S2205). The eNB determines handover of the UE depending on a channelstate of the UE by using the measurement report received from the UE(S2210). If it is determined that handover is not required, the eNBtransmits data to the UE (S2215), and receives ACKnowledgement for thedata from the UE (S2220). If it is determined that handover is requiredfrom the measurement report (S2225), the eNB delivers data of the UE toanother eNB to perform data communication between a new eNB and the UE(S2230 and S2235). Hereinafter, a method for enabling eNB to determinewhether 3GPP access loss has been generated in a UE, by using theaforementioned handover procedure will be suggested. The eNB determinesthat 3GPP access loss has been generated in the UE in case of thefollowing two cases.

First of all, the eNB determines that handover is not required afterreceiving measurement report from the UE (S2240), and transmits data(S2245). However, when the eNB does not receive ACK for the data or anysignal from the UE for a predetermined time (S2250), the eNB determinesthat the 3GPP access loss has been generated in the UE. That is, the eNBdetermines that a channel status of the UE is not bad and thusdetermines that handover to another eNB is not required. However, sincethe eNB does not receive any signal from the UE for a predeterminedtime, the eNB determines that the UE is subjected to the 3GPP accessloss. As signals expected by the eNB to be transmitted from the UE,there may be types of signals for connection recovery in addition to ACKsignal.

Secondly, when the eNB transmits data to the UE (S2260) in a state thatmeasurement report is not received from the UE (S2255) but does notreceive ACK for the data or any signal from the UE (S2265), the eNBdetermines that the 3GPP access loss has been generated in the UE.

If the eNB determines the access loss of the UE in accordance with theaforementioned two cases, the eNB transmits information indicating theaccess loss of the UE to MME. The information indicating the access lossof the UE may be transmitted as being implemented as an access lossindication message, or may be transmitted as being included in anothermessage in the form of a specific indicator.

Subsequently, an example of WLAN access loss will be described withreference to FIG. 23. Access loss of a UE for a TWAN is determined byTWAG. If the access loss is not generated, the TWAG transmits data tothe UE and receives ACK (S2305 and S2310). Meanwhile, if the TWAGtransmits data to the UE (S2335) in a state that adiassociation/deauthentication message is not received from the UE(S2330) but does not receive ACK signal from the UE for a certain timeperiod (S2340), the TWAG determines that the WLAN access loss has beengenerated.

Meanwhile, in respect of the 3GPP access loss of FIG. 22, if the eNBdetermines the access loss in accordance with the aforementioned twomethods, it is not possible to identify that the UE recovers connectionto the 3GPP network or accesses the 3GPP network through another eNB. Inother words, the eNB may determine that the 3GPP access loss has beengenerated even in the case that the UE accesses another eNB by reason ofRLF (Radio Link Failure). Therefore, a problem may occur in that theaccess loss is notified to the PGW through the MME. In this case, aproblem may occur in that the 3GPP access loss is notified to the PGWand therefore the network recognizes that the UE is subjected to theaccess loss in spite of the fact that the UE actually accesses anothereNB. Therefore, a procedure of dropping the 3GPP access loss of the UEwill be described. An example that dropping the 3GPP access loss of theUE is processed by the MME and an example that dropping the 3GPP accessloss of the UE is processed by the SGW will be described.

First of all, the procedure of processing access loss through MME ofnetwork nodes will be described with reference to FIGS. 18 to 20. If astatus described in FIGS. 18 to 20 is generated, the MME dropsinformation on access loss without transmitting the information onaccess loss to the PGW even though the 3GPP access loss is notified fromthe eNB. That is, the MME disregards the information on access loss withrespect to a case which will be described later, and processes that theaccess loss of the UE is not generated.

First of all, if the eNB which has transmitted information indicatingthe access loss of the UE is different from the eNB stored in UE contextinformation of the MME, the MME drops the information on access loss.That is, the MME recognizes that the access loss is not generated in theUE.

Description will be given with reference to the example of FIG. 18,eNB_1 transmits information on access loss of UE_1 to the MME. However,the MME already knows that UE_1 is connected to eNB_2 by contextinformation of UE_1. Therefore, the MME drops the information on accessloss, which is received from eNB_1.

Secondly, if context information of the UE, which is owned by the MME,is requested from another MME, the corresponding MME drops theinformation on access loss. This is because that the MME may know thatthe access loss has not been generated in the UE if it is recognizedthat the UE maintains access to another MME through another eNB.

Description will be given with reference to the example of FIG. 19, theUE accesses eNB_2 even though access to eNB_1 is released. The eNB_1 andthe eNB_2 are respectively connected to MME_1 and MME_2, and the MME_2newly connected with the UE requests the MME of context information ofthe UE, which is owned by the MME_1. Since the MME which has receivedthe request of the context information knows that the UE accesses theeNB_2 even though occurrence of access loss is received from the eNB_1,the MME drops the information on access loss of the UE.

Finally, if the MME does not own context information of the UE, which issubjected to access loss, the MME drops the information on access lossof the UE. That is, the MME disregards the access loss of the UE ofwhich context information is not owned by itself any more.

Description will be given with reference to the example of FIG. 20,cancel location update for the MME_1 may be performed while the UE isnewly being connected to the MME_2. This procedure may be understood asa procedure of deleting UE context information which is owned by theMME_1 as the UE will be connected with the MME_2. When the UE isattached through the MME_2, the context information of the UE, which isowned by the MME_1, is already deleted. Therefore, since the MME_1 knowsthat the UE is attached to another MME even though the information onaccess loss of the UE is received from the eNB_1, the MME_1 drops theinformation on access loss of the UE.

Subsequently, the procedure of processing information on access loss ofthe UE through SGW will be described. If the SGW processes theinformation on access loss of the UE, the MME may transmit theinformation on access loss, which is received from the eNB, to the SGWwithout any determination unlike the description made with reference toFIGS. 18 to 20.

If the MME notifies the SGW of access loss together with identifier(e.g., network ID and/or address of the eNB) of the eNB which hasdetermined the access loss, the SGW processes the access loss on thebasis of the identifier of the eNB and the information on the UE, whichare included in the information on access loss. In more detail, the SGWidentifies S1-U interface of the UE and if eNB set in the S1-U interfaceof the UE is different from the eNB which has indicated the access loss,the SGW drops the information on access loss. If the eNB set in the S1-Uinterface is different from the eNB which has indicated the access loss,it means that the UE is currently connected to another eNB differentfrom the eNB which has indicated the access loss. By contrast, the SGWidentifies the S1-U interface of the UE and as a result, if eNB set inthe S1-U interface is the same as the eNB which has indicated the accessloss, the SGW delivers the information on access loss to the PGW.

Meanwhile, according to the method for determining access loss throughthe SGW, if the SGW connected to the UE is changed, the access loss isdelivered to the PGW without being dropped. Therefore, if theinformation on access loss is received from the SGW, the PGW comparesthe SGW, which is currently connected with the UE, with the SGW whichhas indicated the access loss. That is, the PGW drops the information onaccess loss of the UE if the SGW indicated by the context information ofthe UE is different from the SGW which has indicated access loss.

FIG. 21 illustrates a method for processing access loss when MME ofnetwork nodes senses the access loss.

As described with reference to FIGS. 18 to 20, if the MME transmitsaccess loss to the PGW after sensing the access loss, signaling overheadmay be increased in the network when there are a lot of UEs managed bythe MME. To reduce such overhead, the PGW may establish the MME toindicate access loss only if the UE is operating by being attached tothe TWAN in the SCM.

The PGW may identify a mode of the UE attached to the TWAN, from aaccess mode value of a create session request message transmitted fromthe TWAN. The PGW may establish the MME to report access loss by using achange reporting action information element (IE) included in an updatebearer request message only if the UE is attached to the TWAN in the SCM(S2110 and S2120).

The MME may sense access loss for only a UE, which belongs to a specificgroup, by using subscription information of the UE, and may report thesensed access loss to the SGW and the PGW (S2130 and S2140). On theother hand, the MME may determine whether to report the access loss bydisregarding the details configured from the PGW and using onlysubscription information of the UE. For example, the MME may restrictsignaling overhead of the network by reporting access loss to gold classusers and provide special users with differentiated services.

Also, to reduce signaling overhead, the MME may report access loss onlyif PDN connection supporting NBIFOM is generated in the UE. However,since the MME cannot know that PDN connection of the UE is generated tosupport NBIFOM, the MME may know whether PDN connection supports NBIFOMin accordance with a configuration indicated by the PGW or the UE. Ifthe MME can identify a protocol configuration option (PCO) included inan EPS session management (SM) message, the MME may determine whetherPDN connection supports NBIFOM, even though there is no directnotification from the PGW or the UE.

Although FIG. 21 illustrates an example of reporting access loss throughthe MME, the example of FIG. 21 may similarly be applied to the TWAG.The TWAG may report access loss for only the UE previously configured bythe PGW. The PGW determines whether final access loss is generated, byusing information on access loss, which is received from the TWAG. ThePGW may drop the access loss if a connection request is received fromthe UE through another MME/TWAG within a certain time even though theaccess loss is reported from the eNB/TWAG.

4. Suggested Embodiment 2

Hereinafter, in addition to the aforementioned procedure of processingaccess loss, a procedure of processing data transmitted to a UE whenaccess loss is generated will be described. If access loss is generatedin the suggested embodiments, loss of data transmitted to the UE mayoccur.

FIG. 24 is a diagram illustrating an example of a method for processingdata when 3GPP access loss is sensed, and FIG. 25 is a diagramillustrating an example of a method for processing data when WLAN accessloss is sensed.

First of all, if 3GPP access loss is generated in FIG. 24 (S2455),information on 3GPP access loss is transmitted to the PGW through themethods suggested in FIGS. 18 to 23 (S2405 and S2410). Then, the PGWrecognizes the 3GPP access loss of the UE (S2460). Subsequently, the eNBwhich has reported the 3GPP access loss transmits a tunnel request fordata transfer to the PGW together with information indicating handover(S2415). The PGW generates a tunnel (S2425) by delivering theinformation indicating handover and the tunnel request to the TWAG(S2420), and notifies the eNB that the tunnel has been generatedsuccessfully by transmitting a tunnel request ACK response to the eNB(S2430).

Subsequently, the eNB delivers all data which are being buffered byitself to transmit them to the UE, to the PGW (S2435). The PGW deliversdata, which are available for handover to WLAN, among the data receivedfrom the eNB to the TWAG by means of a routing rule previously set bythe UE (S2440). The TWAG buffers the delivered data (S2465) and waitsfor ending of routing rule update. This is because that the routing ruleof the UE is not updated yet. If the TWAG transmits data to the UEwithout waiting for update of the routing rule, ACK/NACK for thecorresponding data is transmitted from the UE through the 3GPP networkeven though the data is successfully transmitted through the WLAN. Thisis because that the routing rule is not updated yet. If 3GPP access lossis generated, ACK/NACK cannot be transmitted normally. This affects datatransmission in a transport layer (for example, TCP (TransmissionControl Protocol)) or application layer, whereby more retransmissionsand delay time are caused. Therefore, the TWAG should wait for update ofthe routing rule and then transmit data to the UE, whereby datatransmission having no problem may be performed.

The PGW and the UE update the routing rule through the WLAN (S2470). Ifupdate of the routing rule is completed, the PGW transmits a startmarker for notifying the TWAG that the update has been completed, to theTWAG (S2445), and the TWAG initiates data transmission to the UE(S2450).

The 3GPP access loss according to the aforementioned description maysimilarly to be applied to even the case of WLAN access loss shown inFIG. 25. That is, if the WLAN access loss is sensed and reported to thePGW (S2555, 52505, 52510 and S2560), the TWAG transmits informationindicating handover and a tunnel request to the PGW (S2515), and the PGWrequests the eNB of tunnel creation (S2520 and S2525). Subsequently, ifthe PGW notifies the TWAG that tunnel creation has been completed(S2530), the TWAG delivers data to the eNB (S2535 and S2540). The eNBwhich has received the data waits for completing update of the routingrule by buffering data transmission (S2565 and S2570). If the PGWnotifies the eNB that the update of the routing rule has been completed(S2545), the eNB initiates data transmission to the UE (S2550).

FIG. 26 is a diagram illustrating another example of a method forprocessing data when 3GPP access loss is sensed.

According to the embodiment shown in FIG. 26, if occurrence of 3GPPaccess loss of the UE is notified to the PGW (S2650, 52605, 52610 andS2655), the eNB delivers data index not tunnel request to the PGWtogether with information indicating handover (S2615). The data indextransmitted by the eNB may be a value indicating a position or portionof data completely transmitted to the UE through the 3GPP network. Thatis, the eNB may allow the PGW to directly transmit the data, which arebeing buffered, to the UE, by notifying the PGW of the portion of thedata completely transmitted to the UE before the 3GPP access loss isgenerated. In other words, the PGW may determine a position from whichdata should be transmitted to the UE, through the data index valuereceived from the eNB. In the embodiment shown in FIG. 26, instead ofgenerating a tunnel and delivering data from the eNB to the TWAG, aprocedure of allowing the PGW to indicate handover to the TWAG (S2620,52625 and 52630) and delivering data which are being buffered by itselfto the TWAG (S2635) is shown. In other words, handover may be performedwithout new creation of a tunnel. The procedure of allowing the TWAG towait for update of a routing rule after handover and initiating datatransmission if the update of the routing rule is completed is similarto the aforementioned procedure (S2660, 52665, 52640 and S2645).Although the example of the 3GPP access loss is only shown in FIG. 26,the aforementioned procedure may similarly be applied to even the caseof WLAN access loss. If only data index is transmitted without creationof a tunnel, the procedure of generating a tunnel between the eNB andthe PGW or between the TWAG and the PGW may be omitted. Therefore, it isadvantageous that usage of resources between network nodes may bereduced.

5. Device Configurations

FIG. 27 is a diagram illustrating configurations of node devicesaccording to a proposed embodiment.

A user equipment (UE) 100 may include a transceiver 110, a processor120, and a memory 130. The transceiver 110 may be configured to transmitand receive various signals, data, and information to/from an externaldevice. Alternatively, the transceiver 110 may be implemented with acombination of a transmitter and a receiver. The UE 100 may be connectedto the external device by wire and/or wirelessly. The processor 120 maybe configured to control overall operations of the UE 100 and processinformation to be transmitted and received between the UE 100 and theexternal device. Moreover, the processor 120 may be configured toperform the UE operation proposed in the present invention. The memory130, which may be replaced with an element such as a buffer (not shownin the drawing), may store the processed information for a predeterminedtime.

Referring to FIG. 27, a network node 200 according to the presentinvention may include a transceiver 210, a processor 220, and a memory230. The transceiver 210 may be configured to transmit and receivevarious signals, data, and information to/from an external device. Thenetwork node 200 may be connected to the external device by wire and/orwirelessly. The processor 220 may be configured to control overalloperations of the network node 200 and process information to betransmitted and received between the network node device 200 and theexternal device. Moreover, the processor 220 may be configured toperform the network node operation proposed in the present invention.The memory 230, which may be replaced with an element such as a buffer(not shown in the drawing), may store the processed information for apredetermined time.

The specific configurations of the UE 100 and the network node 200 maybe implemented such that the aforementioned various embodiments of thepresent invention can be independently applied or two or moreembodiments can be simultaneously applied. For clarity, redundantdescription will be omitted.

The embodiments of the present invention may be implemented usingvarious means. For instance, the embodiments of the present inventionmay be implemented using hardware, firmware, software and/or anycombinations thereof.

In case of the implementation by hardware, a method according to eachembodiment of the present invention may be implemented by at least oneselected from the group consisting of ASICs (application specificintegrated circuits), DSPs (digital signal processors), DSPDs (digitalsignal processing devices), PLDs (programmable logic devices), FPGAs(field programmable gate arrays), processor, controller,microcontroller, microprocessor and the like.

In case of the implementation by firmware or software, a methodaccording to each embodiment of the present invention can be implementedby modules, procedures, and/or functions for performing theabove-explained functions or operations. Software code may be stored ina memory unit and be then executed by a processor. The memory unit maybe provided within or outside the processor to exchange data with theprocessor through the various means known to the public.

As mentioned in the foregoing description, the detailed descriptions forthe preferred embodiments of the present invention are provided to beimplemented by those skilled in the art. While the present invention hasbeen described and illustrated herein with reference to the preferredembodiments thereof, it will be apparent to those skilled in the artthat various modifications and variations can be made therein withoutdeparting from the spirit and scope of the invention. Therefore, thepresent invention is non-limited by the embodiments disclosed herein butintends to give a broadest scope matching the principles and newfeatures disclosed herein.

INDUSTRIAL APPLICABILITY

The aforementioned method for processing access loss and theaforementioned method for processing data is applicable to variouswireless communication systems that include IEEE 802.16x and 802.11xsystems as well as the 3GPP system. Moreover, the suggested method isapplicable to mmWave communication system that uses ultrahigh frequencyband.

1. A method for processing access loss of a user equipment (UE)operating in a single connection mode (SCM) or a transparent SCM (TSCM)by means of a first network entity operating on a first network, themethod comprising: receiving a measurement report from a UE operating bysimultaneously accessing the first network and a second network;transmitting data to the UE, when it is determined that handover is notrequired for the UE on the basis of the measurement report; determiningthat access loss of the UE for the first network has been generated whenan acknowledgement (ACK) signal for the data is not received from the UEfor a predetermined time; and transmitting the access loss of the UE forthe first network to a second network entity operating on the firstnetwork.
 2. The method according to claim 1, further comprising:determining that access loss of the UE for the first network has beengenerated when an ACK signal for the data transmitted to the UE is notreceived from the UE for a predetermined time in a state that themeasurement report is not received.
 3. The method according to claim 1,wherein the first network is a 3GPP network, the second network is aWLAN (Wireless Local Area Network), the first network entity is an eNB(evolved NodeB) operating on the first network, and the second networkentity is an MME (Mobility Management Entity) operating on the firstnetwork.
 4. A first network entity processing access loss of a UEoperating in a single connection mode (SCM) or a transparent SCM (TSCM)and operating on a first network, the first network entity comprising: atransmitter; a receiver; and a processor operating by being connectedwith the transmitter and the receiver, wherein the processor controlsthe receiver to receive a measurement report from the UE operating bysimultaneously accessing a first network and a second network, controlsthe transmitter to transmit data to the UE if it is determined thathandover is not required for the UE on the basis of the measurementreport, determines that access loss of the UE for the first network hasbeen generated when an acknowledgement (ACK) signal for the data is notreceived from the UE for a predetermined time, and controls thetransmitter to transmit the access loss of the UE for the first networkto a second network entity operating on the first network.
 5. A methodfor processing access loss of a user equipment (UE) operating in asingle connection mode (SCM) or a transparent SCM (TSCM) by means of asecond network entity operating on a first network, the methodcomprising: receiving information indicating the access loss of the UEfor the first network from a first network entity operating on the firstnetwork; determining whether at least one of conditions for dropping theaccess loss is satisfied; and processing that the access of the UE forthe first network is lost when the condition is not satisfied.
 6. Themethod according to claim 5, further comprising: disregarding theinformation indicating access loss when at least one of the conditionsis satisfied.
 7. The method according to claim 5, wherein the conditionsinclude a case that the first network entity which has transmitted theinformation indicating access loss is different from an entity stored incontext information owned by the second network entity with respect tothe UE, a case that the first network entity is requested from anothernetwork node to provide the context information owned with respect tothe UE, and a case that the second network entity does not own thecontent information with respect to the UE.
 8. The method according toclaim 5, further comprising the step of receiving information indicatingprocessing of the access loss in accordance with an operating mode ofthe UE from a packet data network gateway (PGW), wherein the step ofdetermining whether the condition is satisfied includes determiningwhether the condition for dropping the access loss is satisfied only ifthe UE is operating in the SCM or TSCM by identifying subscriptioninformation of the UE.
 9. The method according to claim 5, furthercomprising the step of generating a plurality of groups on the basis ofsubscription information owned by the second network entity, and thestep of determining whether the condition is satisfied is performed onlyif the UE belongs to a group determined to process the access loss amongthe plurality of groups.
 10. The method according to claim 5, furthercomprising the step of receiving information indicating processing ofthe access loss from the PGW depending on whether PDN (Packet DataNetwork) connection of the UE supports NBIFOM (Network Based IP FlowMobility), and the step of determining whether the condition issatisfied includes determining whether the condition for dropping theaccess loss is satisfied only if PDN connection of the UE supports theNBIFOM by identifying subscription information of the UE.
 11. The methodaccording to claim 5, wherein the processing step further includes thestep of transmitting the information indicating access loss to a thirdnetwork entity operating on the first network if the condition is notsatisfied.
 12. The method according to claim 11, wherein the firstnetwork is a 3GPP network, the second network is a WLAN (Wireless LocalArea Network), the first network entity is an eNB (evolved NodeB)operating on the first network, the second network entity is an MME(Mobility Management Entity) operating on the first network, and thethird network entity is an SGW (Serving GateWay) operating on the firstnetwork.
 13. A second network entity processing access loss of a userequipment (UE) operating in a single connection mode (SCM) or atransparent SCM (TSCM) and operating on a first network, the secondnetwork entity comprising: a transmitter; a receiver; and a processoroperating by being connected with the transmitter and the receiver,wherein the processor controls the receiver to receive informationindicating the access loss of the UE for the first network from a firstnetwork entity operating on the first network, determines whether atleast one of conditions for dropping the access loss is satisfied, andprocesses that the access of the UE for the first network is lost whenthe condition is not satisfied.